Linac Laser Notcher Projectin the Proton Improvement Plan (PIP)

David Johnson, Todd Johnson, John Sobolewski, Fred Mach, Kevin Duel, Andrea SaewertFebruary 11, 2014Accelerator Physics and Technology SeminarLinac Laser Notcher Project in the Proton Improvement Plan (PIP)Booster NotchingCurrent Booster Notching SystemLaser Notching (concepts and benefits)Location of current notching experimentPhotoneutralizationRequirements/Techniques for Laser Notching SystemLaser System design and statusBeam Shaping Optical CavityInstallation conceptCurrent PlansIssuesCost/ScheduleSummary

2Topics2/11/2014Accelerator Physics and Technology SeminarBooster utilizes multi-turn injection of H- ions where the Linac pulse length is determined by N*tREV . A notch must be created in the continuous Booster bunch structure to allow for the rise time of the extraction kicker. We need approx 40-50 ns notch.Current technique is to use fast kickers in the Booster to remove a section of the Booster beam (40-50 ns out of ~2.2 ms) at an energy of 400 to 700 MeV and deposit it in a shielded absorber in the ring. New system installed 2013 commissioning underway..Next slide.

3Booster Notching2/11/2014Accelerator Physics and Technology SeminarPictures courtesy of Salah Chaurize4New Booster Notcher Tunnel Devices

Installed just this last shutdown (2013)Commissioning underwayKickers - Long 12Absorber Long 13We would like to create notches outside the Booster tunnel at an energy low enough to eliminate the activation of components entirely (i.e. 750 keV, the energy of the Linac RFQ). This is the basis of this presentationSince the Booster must increase its throughput (x2) to satisfy new demands2/11/2014Accelerator Physics and Technology SeminarLaser Notching of Linac H- Concept/History:Removal of weakly bound outer electron by photodetachment using appropriate laser wavelength, temporal and spatial profile.Concept proven by Ray Tomlin (circa 2001). Next slideAdditional notcher proposals were described in 2005 by Xi Yang to notch the linac beam at the Booster injection RF frequency (FN-0765-AD) and at the revolution frequency utilizing a pumped recirculating cavity (FN-0767-AD). Neither of these proposals were implemented.Most recently proposed by Bob Zwaska and further developed with input from a number of Fermilab colleagues , laser experts, and manufacturers.Benefits:Laser pulses may be formed to match bunch pattern (broad band Fast rise time (may be tailored to individual bunches)Doesnt require high power pulsers /delay lines to create ns pulsesSystem can have a reasonably small footprintAdvances laser technology for accelerator applications (laser stripping, laser notching, laser chopping, photoinjector, laser diagnostics, etc ++++

52/11/2014Accelerator Physics and Technology SeminarIn 2001, Ray Tomlin reported on a successful experiment to create notches in the CW linac beam in the H- 750 keV beam line and have this notch survive at Booster injection.He created a 25 ns notch utilizing a 200 mJ 5 ns laser pulse.To create multiple notches in the linac pulse he proposed a 4 pass bow-tie cavity some 665 meters long (with a storage time of 2.22 ms). Large Pockels cells would shuttle the laser to and from the delay line. A disk gain section would restore optical losses. Average laser pulse energy of 103 mJ Peak power of ~20 MW to strip 99.9% of the ions.This was not implemented.

6First Laser Notching Experiment

2/11/2014Accelerator Physics and Technology SeminarMove loss due to notching OUT of the Booster tunnelMinimum transverse size bunched at 201.25 MHz2/11/20147Location of Linac Notcher in PIP Era

RFQMEBTAccelerator Physics and Technology Seminar7Location of Notcher8

Must fit in this space2/11/2014Accelerator Physics and Technology SeminarExpected Beam DimensionsPhase space simulation at end of RFQ (figure 4.40 of 750 KeV Upgrade Plan)

Trace 3D back calculation of beam size at exit of RFQ based upon emittance measurement at 178 kW power August 9, 2012 CY Tan.Laser beam vertical profile (1/e2) ~ 5 mm.Initial design assumed that the vertical laser beam dimension of 1 cm. Beam measurements indicate vertical laser size could be reduced to 6 mm92/11/2014Accelerator Physics and Technology SeminarPhotoneutralization (1)

The fraction of electrons that are detached from the moving H- ions is:The photon flux (generated by the laser) in the lab frame [photons/cm2/sec]The photon flux in the lab frame is transformed into the rest frame of moving ion as:The interaction (crossing) time is just the ion path length/ ion velocityThe neutralization factor for an ion crossing on axis of the laser beam may be written in terms of lab frame parameters

For q ~ 90o term -> ~g102/11/2014Accelerator Physics and Technology SeminarLinac Beam Bunch Structure24.2 us (~ 11 Booster turns)2.2 us67 ms~22-25 us~5 ns (bunch spacing)~bunch length200 MHz bunch spacing450 kHz notch spacing15 Hz macro pulse rep rateMACROMINI (11 turns)MICRO2.2 us10-12*5ns = 50 -60 ns112/11/2014Accelerator Physics and Technology Seminar

Photoneutralization (2)

Rest frame energy 1.16 eV for 1064 nm laser Cross section 3.66x10-17 cm2

To maximize the neutralization probability->maximize the product

fixed 12To maximize increase pulse energy -> minimize reduce pulse length -> bunch length reduce laser spot size -> ion size

To maximize t for a given H- ion energy increase horizontal laser beam size or increase the number of laser interactions with the ion bunch20-30 mJAssume:Laser size 0.6x6mm

Assume:Laser size 0.6x6mm

~1J1.5 ns60 ns2/11/2014Accelerator Physics and Technology SeminarReduction of Pulse EnergyTo reduce the required pulse energy we can effectively increase the interaction time by utilizing an optical cavity such that the laser interacts with the ion beam multiple times.13H-Linear cavity (zig-zag)Laser follows ion to interact many times (increase t)Cavity length proportional to number of interactionsLaser pulse length = notch lengthCavity dimensions determined by ion velocity and bunch spacingReduces required laser pulse energy by ~ number of interactions

R. Shafer , 1998 BIW2 mJ for 99.92% 2/11/2014Assume mirror reflectivity 99.95%20 reflectionsAccelerator Physics and Technology SeminarRequirementsAll ions in bunch should see the same photon densityThe 201.25 MHz laser pulses must be phased with the RFQThe laser pulse length > bunch length Uniform temporal profileThe burst of 201.25 MHz pulses must match the Booster inj rev. freq.The 450 kHz burst must have appropriate timing within the linac pulseThe pulse energy should neutralize > 99% of ions in each bunch

TechniqueUtilize a CW seed laser and wave-guide modulator to create required laser pulse pattern (both 200 MHz and 450 kHz) at low pulse energies (pJ)Amplify pulse pattern using a three-stage fiber amplifier (nJ to uJ)Further amplify using a free-space solid state amplifier (mJ)Create a spatially uniform photon beam Insert laser pulse into a linear zig-zag interaction cavity where the laser reflections inside the cavity match the ion velocity to reduce required pulse energy by the number N of reflections in the cavity.Requirements and Technique of Laser Notching of H- 142/11/2014Accelerator Physics and Technology Seminar Burst mode seed pulses to Fiber Amplifier followed by Free Space Ampl1=1064nm120 mW CWSW=0.1 nm10 GHz Mach-ZehnderModulatorPulse GeneratorAmplifier, TimingPM FiberLins ~5dBLi~1.8dB15 HzAOMGenerate 24 us burst at 15 hzTRANSPORT BEAM SHAPING OPTICS & OPTICAL CAVITYFiber Pre-AmpFiber Amp 1Fiber Amp 2Free Space AmpOutput modulator/Input fiber pre-amp:201.25MHz pulses (1.25 ns pulse), 458kHz burst Clean up filterIsolatorLine filterFree SpaceGrumman CEO DPSS OEMDiode + TC controlled*Notch 12 bunches -> 60 ns 10 notches/linac pulsePulsed at 15 Hz2/11/201415Accelerator Physics and Technology Seminar16Optical Pattern Generator

Input: 100 mW CW Output: 54 pJ (1.5 ns/200 MHz) 294 uW avg power at 450 kHz

Pulse on/off extinction 30 dB2/11/2014Accelerator Physics and Technology SeminarOPG Fiber Amp Components on Bench

Diode/TEC power supply Safety System interfaceModulator Bias ControllerFiber Pre-ampFiber Amp 1P.S. for RF Amp

172/11/2014Accelerator Physics and Technology Seminar

18New OPG module

Andrea Saewert2/11/2014Accelerator Physics and Technology SeminarOptical Pattern Generation

450.75 kHz burst of 201 MHz pulsesOne set of 201.25 MHz pulsesIndividual 201.25 MHz temporally uniform pulsesPre-distortion of EOM pulses Yellow- AWGPurple- RF Amp outGreen signal form 1.2 GHz (free-space)PD laser pulses out of fiber pre-amplifierAWG: Chase Scientific DA12000 & CG6000 module192/11/2014Accelerator Physics and Technology Seminar20Fiber Pre- Amplifier System

Input 54 pJ 294 mWGain 23 dBGain 17.2 dBOutput 100 pJ 590 mWOutput 385 nJ 2 WPriTel

2/11/2014Accelerator Physics and Technology SeminarGain fiber is Yb doped 6mm core/125 um cladding

System to be re-package in 19 rack mount withComputer control/readback and auto shutdown for YbFA-33 amplifier.ampfilter

21Fiber Amplifier System

Input 363 nJ 1.96 WGain: 14.5 dB

Optical EnginesMicrograph of PCF fiber 2/11/2014Single mode, single polarizationSmall NA (~0.03) Large mode areaHigh peak power levelsHigh pump absorption (~10 dB/m)High reliabilityAccelerator Physics and Technology SeminarSystem on order- due for delivery later this month. Output to include mode stripper (to remove any pump light) and optics to match into first FS amp.22Free Space Amplifier System

Pulsed at 15 HzGain: ~ 23 dB (total for both modules)Output: 2 mJ 10 kW (450 kHZ) 3.2 mW (15 Hz)

Faraday Isolator to protect previous stage and aid in double pass operation.Input: 10 uJ 55W (450 kHz) 16 mW (15 Hz)To Optical Cavity

1D & 2DPSD2/11/2014Class 4 laser systemDifficult to operate with lid offNeed to heavily instrumentAccelerator Physics and Technology SeminarCurrent design -> could change depending of fiber amp performance80923Beam Shaping (modification of the transverse beam profile in the optical cavity)We would like to demonstrate > 99% neutralization efficiency for all ions in the bunch, therefore we would like all ions to see the same photon flux regardless of their transverse amplitude. (i.e roof-top laser profile)

The vertical size of the laser beam should be ~ > 6s of the ion bunch or about 6 mm (the horizontal size should be < 1 mmWe have investigated two techniques to create this roof-top profile through the interaction cavity.pShaper refractive beam shaping opticsBeam stacker splitting a Gaussian beam into H and V polarized beams with a birefringent crystal, a technique proposed by Todd Johnson

2/11/2014Accelerator Physics and Technology Seminar24pShaper (AdIOptica GmbH)Refractive optical system Output beam is free of aberrationCollimated output beamResulting beam profile is stable over large distanceGalilean design

2/11/2014Accelerator Physics and Technology SeminarBeam Shaping w/ pShaper the layout25

Input pShaperOutput pShaperOutput Anamorphic prismCylindrical telescope532nm diodepShaper2/11/2014Accelerator Physics and Technology SeminarIntensity distribution varies with distance due to diffraction effects. For visible light and flattop beam diameter of 6 mm the distance where the deviation in uniformity doesnt exceed +/-10% is about 200-300mm.This distance is inversely proportional to wavelength -> for 1064 nm we should expect only 120 to 180 mm.26pShaper Propagation

2/11/2014Accelerator Physics and Technology Seminar

27pShaper Propagation 2/11/2014We think this would work, butWe would like to do better that this for propagation of a uniform profile.Accelerator Physics and Technology Seminar28Beam Stacker Concept (Todd Johnson)Based upon a birefringentcrystal where the index of refraction is dependent onpolarizationHere the half-wave plate rotates linear polarized beam to 45o and the crystal displaces V pol and H pol remains un-deflected.

2/11/2014

Accelerator Physics and Technology Seminar

29Layout of the Beam Stacker

2/11/2014Accelerator Physics and Technology Seminar

30Telescope to Match Diode to StackerWe use CW diode to test the beam stacker concept. Ultimately the input to the Stacker will be from the Free Space Amplifier.Since the output of the Free Space Amplifier will have a 1/e2 diameter of 5.1 mm we will need a telescope to match the stacker.2/11/2014Accelerator Physics and Technology Seminar31Beam Stacker merging beamlets

2/11/2014

Accelerator Physics and Technology Seminar32Beam Stacker - Propagation2/11/2014

Accelerator Physics and Technology SeminarRepresents 6 mmvertical dimensionwith constant intensity

33Add Cylindrical Telescope to Stacker

2/11/2014Accelerator Physics and Technology SeminarOptical Cavity34

Mirrors at 2.288o wrt H- beam showing 21 interactionsJohn Sobolewski and Fred Mach

H-Laser output to dumpLaser InputMirror separation matched to ion velocity2/11/2014Accelerator Physics and Technology SeminarOptical cavity tests

Fixed mirrorMoveable mirrorTest set-up352/11/2014Accelerator Physics and Technology SeminarOptical Cavity prototypeWe printed a 3D model to test design 36

This was very useful as it pointed out several improvements/modifications to the design.2/11/2014Accelerator Physics and Technology Seminar37Installation

2/11/2014

Accelerator Physics and Technology SeminarIssues:Moveable for MEBT maintenanceElectrical requirementsCooling requirementsEffects of ion source sparkingOptics Box sits on top of rackFree space laser completely enclosed. Currently set for April 2015Goal complete laser in LABend of FY14Finish packaging OPG and testend of FebRepackage Fiber pre-amps(s)end of FebReceive Fiber Amplifierend of FebTest Fiber stages with OPG mid MarchDetermine FA output to determine FSFinalize design of Free Space Amplifierend MarchOrder components for amplifier (14 week delivery for amp modules)Continue optimization of Beam Shapingon goingStart diagnostics electronics design MayFinalize mechanical design of Optical CavityGenerate manufacturing printsmid AprilConstruct optics box stand and relay rackmid March Continue discussion on timing system

2/11/201438Near term PlansAccelerator Physics and Technology SeminarNotch survivability in Booster (see next slides)Start of RF capture Capture parametersNot achieving design pulse intensity (next slides)Reliability of system Impact of ion source sparks on electronics - TBDPortability and alignment Pre-distortion of laser pulses for fiber and DPSS stagesImpact of optical cavity in quad fringe fieldEstimation shows it to be not a problemSimulation electron trajectories by Vladimir Kashikhin

39Issues2/11/2014Accelerator Physics and Technology Seminar

40200 MHz bunches in BoosterTotal time ~ 53 ms injectionChandra Bhat*Measured value in Booster2/11/2014Accelerator Physics and Technology Seminar41Evolution of the Notch in Booster

Total of 17 turns injectedover ~ 34 us

Total time ~ 53 ms of simulation2/11/2014Accelerator Physics and Technology Seminar

42Neutralization vs Pulse EnergyDesign value2/11/2014Accelerator Physics and Technology SeminarWBSTASKM&S*contingency.01.02.03.01Initial Design$0.01.02.03.02Optical Pulse Generator$35,000$6,000.01.02.03.03Fiber Amplification Stage$100,000$16,000.01.02.03.04Free-Space Amplification and optics$160,000$40,000.01.02.03.05Optical cavity and vacuum chamber*$20,000---.01.02.03.06Beam shaping/transport/diagnostics$25,000$5,000.01.02.03.07Timing and Controls$24,000$10,000.01.02.03.08Installation$18,000$6,000.01.02.03.09R&D Lab supplies and materials$7,750----TOTAL (*unburdened)$389,750$83,00043Budget2/11/2014Accelerator Physics and Technology SeminarWe have obligated ~$192K to date. The next largest purchase will be for the free-space amplifier and associated optical components (est. to be ~< $100K).Contingency numbers are amounts above what we expect to spend in each of the Tasks but then there are unforeseen expenses

44Schedule2/11/2014Accelerator Physics and Technology SeminarWe have described our motivation for moving the process of notching outside the Booster tunnel.We have described the requirements for the laser system to create the notches.We have described the laser system design to accomplish the goal of creating notches. We have described the status of the components and system. We have the front-end laser system with the final fiber amplifier on order and are in the process of R&D on beam shaping and working on the final design of the optical cavity.We would like to have laser system operational in lab by end FY14.The current plan is to install the system in Q2 of Fy15.

45Summary2/11/2014Accelerator Physics and Technology SeminarDave BairdDan BollingerKen DomannFernanda GarciaMike KuceraRay LewisBill PellicoPeter PrietoMatt QuinnJinhao RuanJamie SantucciVic ScarpineC.Y. TanBob Zwaska

46Acknowledgements2/11/2014Accelerator Physics and Technology Seminar47Thank you2/11/2014Accelerator Physics and Technology SeminarLaser Parameter Requirements entering interaction chamber: Laser Energy 2.0 [mJoules] Pulse length 1.500000e+03 [ps]Spot size: H 0.0600 [cm] V 0.6000 [cm] Laser beam area 3.600000e-02 [cm^2]Lab Frame Photon wavelength 1064.00 nm Lab Frame Photon Energy 1.868068e-19 [J] 1.165139e+00 [eV] Photons per pulse 1.070625e+16 Photon rate 7.137500e+24 [photons/sec] Photon fluence 2.973958e+17 [photons/cm^2] Photon flux 1.982639e+26 [photons/cm^2/sec] Laser Peak pulse power 1.333333e+00 [MW] 2/11/201448Laser Parameters Accelerator Physics and Technology SeminarDistance between crossings 1.188000e-01 [cm]Distance between reflections on mirror 2.376000e-01 [cm]distance laser travel between crossing 1.487310e+00 [cm]cavity radius 1.486124e+00 [cm] cavity diameter 2.972247e+00 [cm]Incident angle 2.288880e+00 [degrees]Crossing angle 87.71 [degrees] Lorentz Factor 9.992022e-01 Rest frame photon energy 1.164210e+00 [eV] Rest frame wavelength 1.064850e+03 Cross section in rest frame 3.660952e-17 [cm2] 2/11/201449Optical Cavity ParameersAccelerator Physics and Technology Seminarcrossing time 5.015246e-11 [sec]Number of passes 20.000000 Photon flux in H- rest frame 1.981057e+26 [p/cm^2/sec]Mirror Reflectivity 9.995000e-01 Average Neutralization factor per interaction 3.024028e-01 Total Neutralization 9.992551e-01 Multipass insertion length 2.257200e+00 [cm] Total laser path length 5.651779e-01 [m]

2/11/201450Laser/cavity ParametersAccelerator Physics and Technology Seminar

2/11/201451Accelerator Physics and Technology SeminarDPSS output for pump timing2/11/201452Accelerator Physics and Technology SeminarCavity in Quad fringe field

~30 mm5 mm

First quad in doublet is H focusing for H- and e- Assume end-field shape is the same as between pole tipsmirrorsElectron in fringe field